Election after election, Republican and Democratic candidates reap the vote of their party's identifiers. It is relatively rare, in congressional races as well as in the presidential race, for a party nominee to get less than 80 percent of the partisan vote.

"Independents" are less independent than might be assumed. About a third of Americans say they are independents, but about 2/3 say they lean toward one of the parties. Most independents vote in the direction they lean. In the 1970s the number of true independents was larger, and there was a sharp rise in the number of voters who cast a split ticket. Some analysts described this development as a sign of dealignment - a weakening of partisanship.

Polarization declined in both chambers from roughly the beginning of the 20th Century until World War II. It was then fairly stable until the late 1970s and has been increasing steadily over the past 25 years. Congresses 100-112 mark an acceleration of the trend (especially in the House). Note, however, that the acceleration is smooth and does not show a particular jump in polarization induced by the large Republican freshman class elected in 1994. Polarization in the House and Senate is now at the highest level since the end of Reconstruction (Voteview.com).

The high level of polarization was primarily a result of Republicans being more polarized than ever before: